Originally Posted by Christople
my main qeustionthough is do I need something that regulates how much goes in, I want fish in the tank. And how much do drop checkers cost.
Drop checker will tell you that. If your DIY setup doesn't push CO2 past ideal levels then no. Every setup is different, especially with yeast. Diffusion is key. If you are able to get a good diffusion rate then you may get a considerable amount of CO2 in the water. IMO though no you don't need a regulator, not with yeast. It can be regulated in many many ways all by itself. If you get too much CO2 you can change it so diffusion is poorer. Or you could change your mixture to start with less yeast and see if that slows down CO2 production.
The drop checker linked above will work. I prefer the funny bubble glass ones. That one is a bit expensive, but I buy most of my drop checkers, ceramic diffusers, and bubble counters off ebay. Then it takes them half a month to get from china to me, so it evens out I guess